1. Field of the Invention
The present invention relates to a method and apparatus for gear shifting control with improved shift quality during changing from a first gear to a second gear, especially when upshifting.
2. Description of the Related Art
Hydrodynamic-mechanical gear box units are known in a multitude of designs in the form of automatic transmissions for use in motor vehicles. They contain at least one gear branch, which includes a hydrodynamic clutch and a mechanical transmission section, installed in tandem with the clutch. The mechanical transmission section includes rotational speed/torque converters with an appropriate gear ratio, which can be operated through appropriate control elements. Various speeds are achieved by appropriate operation and/or releasing of control elements in the mechanical transmission section. The individual rotational speed/torque converters are preferably in the form of spur gear or planetary gear sets. To shift gears, it is necessary to actuate or release the appropriate control elements of the mechanical transmission section. When shifting up in an automatic transmission, for example, two phases occur, namely the so-called torque phase and an inertia phase. Before the upward shift is effected, the torque input at the transmission clutches includes only the torque which is produced by the combustion engine and which runs through a torque converter. During the torque transfer phase, pressure is exerted on the clutch part that is to be engaged. This torque is divided between the releasing clutch and the engaging clutch. At the end of the torque phase, the torque that is supported by the releasing clutch drops to zero, and the entire torque is transferred to the engaging clutch. After completion of the torque transfer, the phase of transferring the gear ratio, the so-called inertia phase, begins. During this phase, the rotational speed of the combustion engine is quickly reduced to the value of the new gear ratio. This occurs to the same degree in which the pressure of the engaging clutch increases. This produces a large moment of inertia which must be absorbed by the clutch part in addition to the torque that is produced by the combustion engine. This inertia torque produces a torque thrust which is transmitted to the interior of, for example, a vehicle.
A multitude of options are known for the reduction of the torque thrust. One of these options is described as an example in German patent document no. DE 691 13 193 T2. According to the disclosure, control of the shifting procedure is provided by continuously monitoring the input speed at the transmission input shaft and by comparing a change at the end of the torque phase with a stored value. Preferably, the control is improved by delaying the motor's timing of ignition by a certain time. An adaptive control system is provided to adjust the pressure in a device intended for the generation of torque by use of friction for a drive train, which includes a combustion motor and a step-up gear. The system further includes a shaft for input of the torque between the combustion engine and the gear box, an initial friction mechanism for at least partial provision of a first transfer path for the torque between the drive shaft and primary parts of the transmission for the input of torque, and a second friction mechanism which serves to transfer the torque between the drive shaft and secondary parts of the transmission. The system further includes a primary and a secondary pressure operated servo unit which, when under pressure, will operate the first and the second friction mechanisms respectively, whereby the creation of the second transfer path for torque is accompanied by a reduced motor speed. Also included is a device for constantly monitoring the speed at the torque input shaft, that is, at the transmission input shaft, and a device for increasing the pressure of the second servo unit as a response to a command to change the transmission ratio, which requires release of the first friction mechanism and actuation of the second friction mechanism. The system further includes a device for reduction of pressure in the servo unit, as a response to a predetermined measured change in the rotational speed of the torque input shaft, and a device to increase pressure in the servo unit as a result of the reduction in the clutch ability of the first friction mechanism during the shifting procedure. The disadvantage of such a control system is essentially that the necessary adaptation of the pressure progression must occur very sensitively and is therefore very expensive. Adaptation of the pressure value is furthermore always opposite the actual factors at the transmission input shaft, particularly depending on the rotational speed at the transmission input shaft. Changes in the speed and the mass moment of inertia of the combustion engine influence the necessary adaptation of the pressure progression.